PROJECT SUMMARY Sugar mimetics have long been known for their important biological activities. Many of them are currently used in clinics as antimicrobials (e.g., streptomycin, gentamycin, neomycin), antivirals (e.g., oseltamivir, peramivir, entecavir), and anti-diabetics (e.g., acarbose, voglibose). Among naturally-occurring sugar mimetics are the aminocyclopentitols, which contain a five-membered cyclitol unit resembling ribose (ribomimetics). However, due to their broad-spectrum toxicity and/or low production yield, none has yet been developed for clinical use. Therefore, addressing these limitations may provide new paths to the exploitation of their full potential as new drug leads. The long-term goals of this project are to understand the biosynthesis of ribomimetic natural products and to develop new ribomimetic-based drugs to combat infectious diseases. In this proposal, we will focus effort on interrogating the biosynthesis of the ribomimetic-containing antibiotic pactamycin and developing new pactamycin analogs as drug leads against bacteria, viruses, and malarial parasites. Our preliminary data suggest that formation of the pactamycin core structure involves highly unusual discrete polyketide synthases, a broad-spectrum glycosyltransferase, and a radical SAM enzyme. We also found that the tailoring pathway to pactamycin is exceptionally perplexing, due to the activity of numerous promiscuous tailoring enzymes. Furthermore, we have developed genetic, synthetic, and chemo-enzymatic strategies (involving a broad-spectrum ketoacyl-ACP synthase (KAS) III-like protein) to produce new pactamycin analogs and other ribomimetic compounds, some of which have improved biological properties. Here, we propose to: 1) characterize the coordinate function of discrete PKS proteins and the unusual glycosylation of an acyl carrier protein (ACP)-bound polyketide intermediate; 2) decipher the mode of formation of the ribomimetic core, which is predicted to take place via a distinctive biotransformation mediated by radical chemistry; and 3) develop and test new ribomimetic antibiotics for anti-infective activities. Successful completion of this research will advance scientific knowledge and technical capability in the field, and will address the current slow pace of progress in the discovery of new anti-infective drugs, particularly antibacterial, antiviral, and anti-parasitic agents.